Generally, methods of preparing 1,3-butadiene for supply to petrochemical markets include steam cracking, the direct dehydrogenation of n-butene, and oxidative dehydrogenation of n-butene. However, since the steam cracking process, which is responsible for 90% or more of the butadiene that is supplied, is not a single process for producing butadiene, it is problematic in that a new naphtha cracker should be introduced to fulfill the increased butadiene demand, and thus the raffinate components, other than butadiene, are further produced. In addition, the direct dehydrogenation of n-butene, which is an endothermic reaction, is unsuitable for use in commercial processes because it requires conditions of high temperature and low pressure for reaction and results in poor thermodynamic properties and very low yields [L. M. Madeira, M. F. Portela, Catal. Rev., vol. 44, p. 247 (2002)].
Hence, the oxidative dehydrogenation of n-butene for producing 1,3-butadiene is regarded as a useful alternative that enables the production of 1,3-butadiene through a single process. In particular, when a C4 raffinate-3 or C4 mixture is used as the source of n-butene, it is advantageous in terms of adding high value to the surplus C4 raffinate components. Specifically, the C4 mixture used as the reactant in the present invention is an inexpensive C4 raffinate remaining after the separation of useful compounds from a C4 mixture produced through naphtha cracking. More specifically, a first mixture remaining after extracting 1,3-butadiene from a C4 mixture produced through naphtha cracking is called raffinate-1, a second mixture remaining after extracting isobutylene from the raffinate-1 is called raffinate-2, and a third mixture remaining after extracting 1-butene from the raffinate-2 is called raffinate-3. Therefore, the C4 raffinate-3 or C4 mixture is composed mainly of 2-butene (trans-2-butene and cis-2-butene), n-butane, and 1-butene.
The oxidative dehydrogenation of n-butene (1-butene, trans-2-butene, cis-2-butene) is a reaction between n-butene and oxygen that produces 1,3-butadiene and water. This reaction is thermodynamically advantageous because stable water is produced as a product, and is also commercially advantageous because the reaction temperature may be decreased. However, in the above reaction using oxygen, many side-reactions, including complete oxidation, etc., are supposed to occur. Thus, there is an urgent need for the development of a catalyst that maximally inhibits such side-reactions and has high selectivity for 1,3-butadiene. The catalysts for use in the oxidative dehydrogenation of n-butene, known to date, include ferrite-based catalysts [J. A. Toledo, M. A. Valenzuela, H. Armendariz, G. Aguilar-Rios, B. Zapzta, A. Montoya, N. Nava, P. Salas, I. Schifter, Catal. Lett., vol. 30, p. 279 (1995)/W. R. Cares, J. W. Hightower, J. Catal., vol. 23, p. 193 (1971)/R. J. Rennard, W. L. Kehi, J. Catal., vol. 21, p. 282 (1971)], tin-based catalysts [Y. M. Bakshi, R. N. Gur'yanova, A. N. Mal'yan, A. I. Gel'bshtein, Petroleum Chemistry U.S.S.R., vol. 7, p. 177 (1967)], bismuth molybdate-based catalysts [A. C. A. M. Bleijenberg, B. C. Lippens, G. C. A. Schuit, J. Catal., vol. 4, p. 581 (1965)]/Ph. A. Batist, B. C. Lippens, G. C. A Schuit, J. Catal., vo.5, p. 55 (1966)]/W. J. Linn, A. W. Sleight, J. Catal., vol. 41, p. 134 (1976)/R. K. Grasselli, Handbook of Heterogeneous Catalysis, vol. 5, p. 2302 (1997)].
Among these catalysts, the bismuth molybdate catalyst is present in various phases, and, in particular, three phases, including α-bismuth molybdate (Bi2Mo3O12), β-bismuth molybdate (Bi2Mo2O9), and γ-bismuth molybdate (Bi2MoO6), are known to be usable as catalysts [B. Grzybowska, J. Haber, J. Komerek, J. Catal., vol. 25, p. 25 (1972)]. Furthermore, β-bismuth molybdate (Bi2Mo2O9) and γ-bismuth molybdate (Bi2MoO6) are known to have superior activity for the oxidative dehydrogenation of n-butene compared to that of α-bismuth molybdate (Bi2Mo3O12) [Ph. A. Batist, A. H. W. M. Der Kinderen, Y. Leeuwenburgh, F. A, M. G. Metz, G. C. A. Schuit, J. Catal., vol. 12, p. 45 (1968)/A. P. V. Soares, L. K. Kimitrov, M. C. A. Oliveira, L. Hilaire, M. F. Portela, R. K. Grasselli, Appl. Catal., vol. 253, p. 191 (2003)]. The bismuth molybdate catalyst takes the form of various phases depending on the preparation conditions thereof, and furthermore, upon the preparation of the catalyst, controlling the pH enables the precise control of the phase of the resulting catalyst.
Some patents and literature have reported bismuth molybdate-based catalysts for the oxidative dehydrogenation of n-butene. More specifically, in regard to the production of 1,3-butadiene using pure bismuth molybdate, many reports have been made of the oxidative dehydrogenation of 1-butene at 420° C. using a mixed-phase bismuth molybdate catalyst comprising β-bismuth molybdate and γ-bismuth molybdate, resulting in a maximum yield of 1,3-butadiene of 28.9% [A. P. V. Soares, L. K. Kimitrov, M. C. A. Oliveira, L. Hilaire, M. F. Portela, R. K. Grasselli, Appl. Catal., vol. 253, p. 191 (2003)], of the oxidative dehydrogenation of 1-butene at 415° C. in the presence of each of a β-bismuth molybdate catalyst and a γ-bismuth molybdate catalyst, resulting in the yields of 1,3-butadiene of 51.7% and 56.4%, respectively [P. Boutry, R. Montamal, J. Wrzyszcz, J. Catal., vol. 13, p. 75 (1969)], and of the oxidative dehydrogenation of 1-butene at 422° C. using a β-bismuth molybdate catalyst, resulting in the yield of 1,3-butadiene of 55% [Ph. A. Batist, A. H. W. M. Der Kinderen, Y. Leeuwenburgh, F. A, M. G. Metz, G. C. A. Schuit, J. Catal., vol. 12, p. 45 (1968)].
Moreover, patents related to the preparation of complicated multicomponent-based metal oxide catalysts for use in the preparation of 1,3-butadiene at high yield have been reported [S. Takenaka, A. Iwamoto, U.S. Pat. No. 3,764,632 (1973)/S. Takenaka, H. Shimizu, K. Yamamoto, U.S. Pat. No. 3,966,823 (1976)/S. Takenaka, H. Shimizu, A. Iwamoto, Y. Kuroda, U.S. Pat. No. 3,998,867 (1976)/M. Arakawa, H. Yoshioka, K. Nakazawa, U.S. Pat. No. 4,504,692 (1985)/H. Yamamoto, K. Okumura, U.S. Pat. No. 4,595,788 (1986)].
The use of the multicomponent-based metal oxide catalyst disclosed in the above literature leads to very high yields of 1,3-butadiene, but is commercially disadvantageous because it is considerably difficult to synthesize the multicomponent-based metal oxide catalyst, and it is also difficult to assure reproducibility. Further, in the case where the C4 mixture is used as a reactant, the constituents of the catalyst are complicated, and thus cause many side-reactions with the components included in the C4 mixture, undesirably greatly changing the catalytic activity and the 1,3-butadiene selectivity.
In addition, one of the problems with the oxidative dehydrogenation of n-butene is that the use of the reactant containing a predetermined amount or more of n-butane results in decreased yields of 1,3-butadiene [L. M. Welch, L. J. croce, H. F. Christmann, Hydrocarbon Processing, p. 131 (1978)]. Thus, in order to overcome the problem occurring when using the C4 mixture as a reactant, the above conventional techniques are limited to the catalytic reaction using only pure n-butene (1-butene or 2-butene) as the reactant. Even in an actual commercial process using a ferrite catalyst, a C4 mixture, in which the amount of n-butane is maintained low, that is, less than 5 wt %, is used as a reactant. As such, in order to use pure n-butene, a process of separating n-butene from the C4 mixture is additionally required, inevitably drastically decreasing economic efficiency.
As mentioned above, the literature or patents related to the catalyst and process for preparing 1,3-butadiene through the oxidative dehydrogenation of n-butene are characterized in that pure 1-butene, 2-butene or a mixture thereof is used as the reactant, or otherwise, a very complicated multicomponent-based metal oxide is used as the catalyst. However, cases in which 1,3-butadiene is prepared using a C4 raffinate, including a high concentration of n-butane-containing C4 raffinate-3 or C4 mixture, as a reactant, in the presence of a mixed-phase bismuth molybdate catalyst comprising single-phase bismuth molybdate catalysts have not yet been reported.